Automated clinical chemistry analyzers are well known in the art and generally use an aspirating device such as a sampling tip, probe or needle to transfer predetermined volumes of liquid samples or reagents between different receptacles, such as sample containers, reagent containers and reaction cuvettes positioned at various locations on the analyzer. The aspirating device, commonly referred to as a sample or reagent probe, is usually an elongated, needle-like component having a hollow passage whereby liquid may be drawn into and dispensed from the sample or reagent probe using an appropriate pump. Such sample or reagent probes may be used to aspirate and deliver liquid samples or reagents between different receptacles, either with the same liquid sample or reagent probe or with multiple probes.
A common problem in such aspirating probes is the risk of liquid carryover, which usually occurs when a probe having residual traces of a previously dispensed sample or reagent is introduced into the volume of a different sample or reagent, thereby interfering with subsequent analyses.
To reduce carryover, the liquid handling probe is typically cleaned by washing between successive cycles of operation. Probe washing may be accomplished, for example, by lowering the liquid handling probe into a wash cell that contains an appropriate wash fluid solution. The wash fluid solution directly washes the exterior of the probe, whereas the interior of the probe may be cleaned by aspirating and discharging the wash fluid solution. Alternatively, the probe may be cleaned by flushing a wash fluid from a separate wash fluid reservoir through the probe. In this manner, the volume of carryover on the exterior surface and/or the interior surface of the probe may usually be reduced.
A common problem with probe washing, however, is observed when residual sample or reagent is absorbed on the surface of the probe despite washing. This residual material may mix with subsequent samples or reagents drawn into the liquid handling probe and interfere with chemical analyses. Furthermore, the presence of additional residual droplets of sample or reagent on the interior and/or exterior surface of the probe may introduce unwanted additional volume of liquid into a destination receptacle, which is particularly problematic when sample volumes themselves are relatively small.
Another common problem with probe washing is the amount of time and the volume of wash fluid required to adequately clean the probe. Depending on the nature of samples or reagents, numerous lengthy wash cycles may be required, and large volumes of wash fluid may have to be flushed through the probe to achieve a desired degree of reduction in residual carryover. This is particularly problematic with clinical samples such as human blood or serum, since disposing of a large volume of biohazardous waste can be expensive and logistically difficult.
One possible solution to these problems is described in U.S. Pat. No. 5,506,142 and in its European counterpart EP0571611. These patents disclose a probe wash system and method of using the system wherein a turbulent, segmented flow of gas and fluid created in the probe by the simultaneous introduction of pressurized air and water is used to blow a residual carryover material out of the probe prior to washing the probe with additional wash fluid. One significant problem with such a system is that it is known to generate bubbles, which can become trapped inside the probe and subsequently introduced into a test chamber, thereby negatively affecting the accuracy of subsequent measurements. Thus, there remains a need for better devices and methods that would address the aforementioned limitations of existing probe cleaning technologies.
In this regard, an improved apparatus and method for cleaning a liquid handling probe that minimize carryover of material between different samples or reagents are disclosed herein. The disclosed embodiments effectively decrease the amount time needed to achieve the desired low levels of carryover and/or reduce the volume of wash fluid required to achieve the desired low levels of carryover between different samples or reagents.